Electromagnetic device



June 1 1926. 1,586,885

G. w. ELMEN ELECTROMAGNETIC DEVICE Filed August 16. 1921 B B v 4 H3 H| H2 H6H4H5 //7 van for: Gasmf W [/men.

by W /Wy Patented June 1, 1926.

UNITED STATES PATENT OFFICE.

GUSTAE W. ELMEN, OF LEON IA, NEW JERSEY, ASSIGNOR T WESTERN ELECTRIC COM- PANY, INCORPORATED, 01 NEW YORK, N. Y., A CORPORATION OF 'NEW YORK.

ELECTROMAGNETIC DEVICE.

Application filed August 16, 1921. Serial No. 492,721.

This invention relates to frequency multipliers or harmonic producers of the type in which cyclically varyin flux is set up 1n a magnetic circuit or circuits in part at least 6 by a cyclically varying current, in such manner that the permeability varies during the cycle, the varying flux inducing secondary currents containing components whlch are harmonics of the inducing current. These 10 devices are ordinarily designated static frequency changers to distinguish them from the dynomo-electric machine type. An example of the static type which is chosen herein for illustration, employs two magnetic circuits upon which the inducing variable field andalso a. constant direct field are impressed. These magnetic circuits have a common output circuit and are so associated with the inducing flux and with the output circuit that output current having double the frequency of the inducing flux is set up. The invention provides an improved magnetic circuit for such frequency changers and makes use of a magnetic material characterized by high permeability, especially at low magnetizing forces, and by low hysteresis losses.

Heretofore iron and silicon steel have been employed generally in electromagnetic devices, in order to secure high permeability at the forces produced by the currents.

passing therethrough; while the principal possible rivals of iron, namely nickel and cobalt, have found but little application due to their inferior characteristics. lVith nickel and cobalt in this respect stands Heuslers alloy of aluminum, manganese and copper. It has been found that a composition of about two-thirds nickel and one-third copper, when tested at low magnetizing forces, gives a permeability higher than that of iron alone. iVith the exception of aluminum, all these metals stand close together in their atomic weights and atomic numbers, and in this specification these five elements, manganese, iron, cobalt, nickel and copper, having these consecutive atomic numbers, 25, 26, 27, 28, 29, will be regarded as belonging to the magnetic group of elements.

The criterion of high permeability is not the only one to be considered in seeking the best magnetic material for use in such electromagnetic devices. If the magnetizing forces and the resultant flux are changed 5 rapidly, then for most purposes the material should exhibit a low hysteresis loss. The development of eddy currents under these couditlons may be obviated to a considerable extent by lamination; but the resistivity of the material is a factor which may be of importance in this connection; the higher the resistivity the more the eddy current loss will be kept down.

The description hereinafter given is made specific to the employment in a magnetic fre quency changer of a new magnetic material comprising elements of the magnetic group combined in suitable proportions, which when subjected to a proper heat treatment and guarded against undue stresses and other disturbing causes, develops and retains an extremely high permeability at low magnetizing forces and a low hysteresis loss.

Iron and nickel are fused together in an induction furnace in the proportions of about 21 75 iron and 7 8 71; nickel; Good commercial grades of these metals are suitable for this purpose. The molten composition is poured into a mold and cooled either in the form in which it is ultimately to be used or in a convenient form to be worked over for that purpose. In the latter case it may be swaged or drawn or rolled. When desired to be laminated, some such manner of working the material to the required form may be necessary.

\Vhile 78 and 21 have been mentioned as giving the proportion of the ingredients, nickel and iron, to be employed in making up the improved magnetic material, it will be understood that the proportion may deviate considerably from these figures when nickel and iron are the only ingredients, and that when there are other ingredients this proportion may not apply. Up to the present time when the only ingredients are nickel and iron, it has been found that a proportion about the same as that named, gives the greatest permeability for low magnetizing forces. Other ingredients than nickel and iron may be employed for various purposes, not only to confer high permeability on the product, but for other objects: for example, it may be desirable to add chromium for the reason that a comparatively small quantity of this element will cause a decided increase in the resistivity of the composition, and this high resistivity may be a desirable factor to cut down the eddy current losses in the magnetic material. A composition of nickel iron 34%, and chromium 11%, has been carefully prepared, heat-treated and tested, and has been found to give a high value of permeability at low magnetizing forces.

These new alloys comprising nickel and iron or other elements of the magnetic group to which reference is made above, are fully described'and claimed in the application of G. W. Elmen, Serial No. 473,877, filed May 31, 1921.

To develop the utmost permeabiht in the magnetic material the cores may e subjected to a heat treatment, the treatment required in any particular case varying somewhat as regards temperatures employed and duration of heating and cooling. The optimum values of these variables may be readily determined in any specific case by experiment. A suitable heat treatment to develop high permeability has been found to be to heat the material to a temperature that will be suitable for annealing, then to cool at an optimum rate that must be determined by experiment. After the heat treatment,

'the material should be guarded against any considerable strains. To avoid strains incident to forming or shaping the material, the heat treatment is applied to the material in a form ready for assembly in the apparatus in which it is to be used.

Measurements of the permeability of nickel-iron compositions of other proportions than that here stated have shown that the departure may be considerable without serious impairment of the permeability. Under similar test conditions, for 70 per cent nickel instead of 78 per cent, after proper annealing and cooling, the permeability at forces approaching zero, is about 4100, and at a magnetizing force of 0.2 c. g. s. unit the permeability is about 15,000 whereas for a percentage of 78 the respective values of permeability are 7000 and38,500. It will be seen that these values are much higher than for silicon steel at the same magnetizing forces which has respec-' tive permeabilities of only about 400 and 1500. Thus a wide departure may be made from the proportion named, yet the permeability at low magnetizing forces will be far greater than for the best materials of the prior art.

force. The maximum permeability so far attained is between 45,000 and 60,000. This occurs with the 7 8 per cent nickel compo sition at a magnetizing force of about"0 .1 c. g. s. unit, and the corresponding value of the induction B being from 4,500 to 5,000 c. g. s. units.

Referring to the drawings, Fig. 1 shows one type of frequency changer; Fig. 2 shows the magnetization curve for iron; and Fig. 3 shows the ma netization curve for a composition of nic el and iron.

A source of alternating current 1 is connected to two coils 2 and 3 wound on magnetic cores 4 and 5, respectively. The coils 2 and 3 are oppositely Wound. Coils 6 and 7 which are also wound on the cores 4 and 5, respectively, are connected through a suitable impedance 8, battery 9 and variable resistance 10. Coils lland 12 constitute the secondary coils and in them is to be induced a current having double the frequency of that in coils 2 and 3.

By means of the battery 9 and the variable resistance 10, the direct current passing through the coils 6 and 7 is so regulated that the magnetizing forces thus produced will be sufficient to give rise to a certain magnetic induction in cores 4 and 5. This may be more readily understood from Fig. 2. The desired magnetizing force is H and the magnetic condition of the cores will be that represented by the point 13 on the curve. This point, as will be apparent, is on the knee of the magnetization curve. Now the result of passing an alternating current through coils 2 and 3 from the source 1, will be to alternately increase and decrease the magnetizing force exerted on the cores and thus cause a change in the magnetic induction thereof. When the positive half of the cycle of the alternating current exerts its influence on the cores, there will be a very gradual rise in flux therein, while when the negative half of the cycle of the alternating current exerts its influence on the cores there will be a sharp diminution in the magnetization. These relative changes may be seen by assuming in Fig. 2 that the increase in magnetizin force in the positive half of the cycle is -H and the decrease in the negative half of the cycle is H,H corresponding to an increase of magnetic induction B B,, and a decrease of B,B respectively. The resulting effect, inasmuch as coils 2 and 3 are in series and are oppositely wound, is to produce in the coils 11 and 12 a current having double the frequency of that in the coils 2 and 3.

Fig. 3 shows the magnetization curve for a nickel-iron composition having approximately 78 nickel and 21 iron. It will be noted that the composition becomes saturated at a much lower magnetizing force than iron, and also that the curve is very much steeper than that in Fig. 2. These two differences make the nickel-iron composition more suitable as a magnetic material for the magnetic cores in frequency changers.

Instead of necessitating the employment of a direct current of a value of H in order to bring the material into the desired condition, when the nickel-iron compositions are used, only H c. g. s. units are required. This large saving in direct current for magnetization purposes, will alone make it desirable to construct magnetic cores of nickel and iron. The relative changes in this case may be understood by assuming in Fig. 3 that the increase in magnetizing force in the positive half of the cycle is 11 -11 and the decrease in the negative half of the cycle is H H corresponding to an increase of magnetic induction B B and a decrease of B -B respectively.

The alternating current flowing through I the coils 2 and 3 will produce eddy currents in the magnetic cores, the energy of such currents being thereafter dissipated as heat. The eddy current loss varies as the square of the flux density. From a consideration of the two curves shown in Figs. 2 and 8, and from what has been set forth hereinabove, it will be apparent that a core in accordance with this invention will have a much lower eddy current loss at saturation than an ironcore; Thus by utilizing the core of this invention, there is comparatively little heat developed, resulting from the eddy current loss. This eddy current loss I will also be greatly diminished due to the "extremely high specific resistance of the magnetic compositions described above.

The magnetic compositions herein described have a much lower hysteresis loss than iron when subjected to a low magnetizing force. On accountcof this fact a much more rapid magnetization in alternate directions, with minimum production of heat will be possible of attainment.

While particular compositions have been referred to herein specifically, it is to be understood that other magnetic compositions which show the characteristics hereinabove described, are considered to be within the scope of the invention.

What isclaimed is:

1. A static frequencyw multiplying device having a magnetic circuit element of material consisting chiefly of nickel and iron and having higher permeability at forces just having a magnetic circuit element of material consisting chiefly of nickel and iron and having maxlmum permeablllty at magnetizmg forces less than two-tenths of a gauss,

the permeability being greater than for iron,

in this region, and means for causing the flux in said element to vary periodically and cyclically between limits which include the knee of the magnetization curve.

3. A static frequency multiplying device having a magnetic circuit element of material consisting chiefly of nickel and iron, the nickel content comprising within a few per cent of 78 per cent of the magnetic element content, and means for periodically and cyclically varying the flux in said element between limits which include the knee of the magnetization curve of said material.

4. An electromagnetic frequency multiplier of the static type comprising an alternating current circuit and a direct current circuit, and in inductive relation with said circuits a plurality of magnetic elements each composed of material consisting chiefly of nickel and another element of the magnetic group, and-having higher permeability than iron at magnetizing forces around two tenths of a gauss or less and having a lower saturation point than iron, the flux in said magnetic elements being periodically and cyclically varied by the current in said circuits between limits including the knee of the magnetization curve of said material.

5. A magnetic device comprising a coil and a core therefor of a magnetic alloy consisting chiefly of nickel and iron, said core having a higher permeabilitythan iron for magnetizing forces of a few tenths of a gauss and less and having saturation at a lower value of applied magnetizing force than iron, and means for applying alternating currents to said coil of such a value that at least one-half wave of the resultant flux is limited by saturation.

In witness whereof, I hereunto subscribe my name this 10th day of August A. D., 1921.

GUSTAF w. EYLMEN. 

